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-   -   What is diffrence between I386 and I486? (

Electro 05-29-2006 05:23 PM

The 80x86 is model instruction. Every model that comes out includes new instructions and new ways of handling the data with out hurting backward compatiblity. An 80386 instruction can be run on a 80386 and up to a 80786. Everybody mistaken Pentium 4 as 80686 but they are actually 80786. If you compile the code on Pentium 4 using 80786 model, the program will not work on 80686 and lower. The name Pentium is an 80586 because the prefix Penti means five and um means powerful (I think).

No, the 80386 code will not hurt an 80686 system.


Originally Posted by chadwick
I'm now convinced that running the 386 kernel on my 686 machine was causing a problem which is discussed in another thread:

Wrong, I have never had any problems running 80386 on a 80686 processor. It is actually the controller and faulty hard drive. Maxtors hard drives are very problematic drives. I recommend Hitachi or Western Digital. Also in some systems mult-mode may have to be enabled by the kernel to fix the problem.

saturndude 05-29-2006 07:33 PM

The difference?

My first PC was a 386DX-40. As I remember, the 486 had four processor instructions that the 386 did not have. These four (IIRC) were combinations of 386 instructions, so what had taken 2 instructions on a 386 now only required one (and may be faster with just one).

Intel's 386 had 275,000 transistors, AMD's had 280K. I've heard you could push AMD's 40 MHz chip up to 80 MHz without damage, but don't quote me on that.

And please don't ever use one of those 486 SXLC or 486 DXLC chips, unless you know what you are doing. They do NOT have all the CPU registers that a true 486 has -- so if your program wishes to use all the registers of a 486 to store stuff, the program will crash!

So to answer your question, running a 386 program on a 486 (or higher) may mean the program uses more instructions to get the job done because it doesn't issue one of those four "combined" instructions, or any instructions that the Pentium, AMD K5, K6, or later chips know how to carry out.

Also "i386" can be used to mean "Intel / AMD Pentium-class instructions" to differentiate the files from Linux for Apple PowerPC (PPC). I suspect that Mandrake (or others) may have used "i386" this way (around Mandrake 8.0 or 8.2).

Hope this helps.

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